What Size Conduit Do I Need for Three #2 AWG and a #8 Ground?

A user asked the app what conduit size fits three #2 AWG conductors and a #8 ground. Assuming THHN or THWN insulation, the answer is 1 1/4 inch for both EMT and Schedule 40 PVC. Here is how the math works so you can rerun it for any combination.

Step one: add up the conductor areas

Chapter 9, Table 5 of NEC 2023 lists the approximate area of each insulated conductor. A #2 THHN is 0.1158 square inches and a #8 THHN is 0.0366 square inches. Three #2 conductors total 0.3474, and adding the #8 ground brings the bundle to 0.3840 square inches. The equipment grounding conductor counts toward fill just like any other conductor, a detail Chapter 9 Note 3 makes explicit.

Step two: apply the 40 percent fill limit

With more than two conductors in a raceway, Chapter 9, Table 1 limits fill to 40 percent of the conduit's internal area. Table 4 lists the 40 percent numbers directly. For EMT, the 1 inch trade size offers 0.346 square inches at 40 percent, which is short of our 0.384. The 1 1/4 inch EMT offers 0.598 square inches, plenty of room. Schedule 40 PVC is slightly tighter than EMT, with 1 inch at 0.333 and 1 1/4 inch at 0.581, so the answer stays 1 1/4 inch. Rigid and IMC land the same way. If you were pulling XHHW instead of THHN the #2 area grows slightly, but 1 1/4 inch still holds all four.

Worth a thought before you bend

Fill is the code minimum, not the comfort number. A 60 percent filled 1 1/4 inch run with three 90 degree bends pulls hard, and long pulls with #2 copper are heavy. Many electricians jump to 1 1/2 inch on runs over 100 feet purely to save their shoulders. Also confirm your ground size against 250.122. A #8 copper equipment ground covers overcurrent devices up to 100 amps, which matches the typical use of #2 copper feeders on 100 or 115 amp breakers.

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